IMAGE  EVALUATION 
TEST  TARGET  (MT-S) 


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Photographic 

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CIHM/ICMH 

Microfiche 

Series. 


CIHM/ICMH 
Collection  de 
microfiches. 


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10X  14X  18X  22X 


12X 


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H 


24X 


28X 


32X 


re 

Idtails 
}s  du 
nodifier 
)r  une 
ilmage 


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les 


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dernidre  image  de  cheque  microfiche,  selon  le 
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de  Tangle  sup6rieur  gauche,  de  gauche  d  droite, 
et  de  haut  en  bas.  en  prenant  le  nombre 
d'images  n^cessaire.  Les  diagrammes  suivants 
illustrent  la  m^thode. 


'  errata 
d  to 

It 

e  pelure. 

;:on  d 


n 


32X 


1 

2 

3 

1 

2 

3 

4 

5 

6 

I  in    ■   -I  III  ■  iiaiii       ^iiiliilUBIWwmijiiiii  iliiniii 


L 


mtmimiimmtimttW'""'  "<*'' 


A  CONTRIBUTION 


TO  TIIK  STITDY  OK 


DOUBLE  SALTS  IN  WATER  SOLUTION. 


DISSERTATION 


SUBMITTED  TO  THE  BOARD  OF  UNIVERSITY  STUDIES  OF 


THE 


;    JOHNS     HOPKINS    UNIVERSITY  FOR   THE         iv^f 


•v-v»?, 


'? 


^- 


DEGREE  OF  DOCTOR  OF  PHILOSOPHY, 


-BY- 


KBENEZER   MACKAY 


7V 


1896 


KASTON,  PA.: 
CHEMICAL    I'VBLISHINO  COMPANY. 

1S97. 


'^ 


-  /"   t 


stuB-jn^'A  rjai-.^  :.,'>-ir-;,i'-*;^ 


^ 


V 


CONTENTS. 


Introduction 

Conductiviiy  apparatus 

Solutions 

Conductivity  Measurement 

Method  of  Titrating  Aluminium 

Alums 

Conductivity  Results 

Potassium  Sulphate 

Aluminium  Sulphate 

Chromium  Sulphate 

Potassium  Aluminium  Alum 

Sodium  Aluminium  Alum 

Ammonium  Aluminium  Alum 

Potassium  Chrome  Alum 

Ammonium  Chrome  Alum 

Green  Modification  of  Ammonium  Chrome  Alum 

Ammonium  Iron  Alum 

Stability  of  Alums  in  Dilute  Solution 

Comparison  of  Conductivity  Results 

Summary  of  Conductivity  Results 

Freezing-point  Measurements 

Comparison  of  Kreezing-Poiiit  Results 

Double  Chloride  of  Zinc  and  Potassium 

Preparation 

Conductivity 

Conclusion 

Biographical 


riiRc. 

•  5 
.   lo 

II 
II 

12 

•  13 
'3 

•  '3 

•  14 
.  i6 

•  17 

•  '7 
.   i8 

•  '9 

•  '9 

.  20 

.  20 

.  20 

.  21 

•  27 
.  .   28 

■  30 

•  32 

•  32 

•  33 

•  34 

■  35 


"•i~;r~n: 


ACKNOWLEDGMENT. 
The  author  wishes  to  express  his  sense  of  gratitude 
to  Professor  Remsen,  both  for  class-room  instruction  and  for 
'the  helpful  suggestion  and  encouragement  received  from  him  ; 
to  Professor  Morse  and  Professor  Renouf  for  the  benefit  de- 
rived from  their  instruction  ;  and  to  Doctor  H.  C.  Jones,  at 
whose  suggestion  this  work  was  undertaken,  for  valuable  ad- 
vice and  constant  experimental  assistance  throughout  its 
progress.  He  also  wishes  to  express  his  appreciation  of  the 
instruction  received  from  Professor  Ames,  Professor  Frank- 
lin and  Doctor  Hulburt. 


A 


\ 


se  of    gratitude 
truction  and  for 
ceived  from  him  ; 
r  the  benefit  de- 
ll. C.  Jones,  at 
for  valuable  ad- 
throughout    its 
preciation  of  the 
Professor  Frank- 


Introduction. 

If  a  solution  of  a  mixture  of  two  salts  having  a  common  ion 
be  subjected  to  crystallization,  the  two  salts  may  crystallize 
out  separately  or  crystals  may  form  containing  both.  In  the 
latter  case  two  modes  of  separation  are  to  be  distinguished, 
according  as  the  crystals  formed  are  of  variable  or  of  constant 
composition.  When  of  variable  composition  they  are  mixed 
crystals,  or  isomorphous  mixtures.  When  the  constituent  salts 
are  present  in  constant  molecular  proportions,  the  crystalline 
compound  is  a  double  salt.  The  constancy  of  composition  of 
the  crystals  of  a  double  salt  raises  the  question  whether  the 
double  salt  is  present  as  such  in  solution  or  is  first  formed 
only  at  the  moment  of  crystallization. 

The  question  of  the  existence  of  double  salts  in  solution 
has  attracted  the  attention  of  many  investigators,  and  a 
variety  of  methods  have  been  employed  in  the  investigations. 
The  chief  methods,  classified  according  to  the  phenomena  or 
properties  investigated,  may  be  grouped  according  as  they 
relate  (a)  to  diffusion;  (b)  to  thermal  changes;  (c)  to  volume 
changes;  (d)  to  solubility;  (e)  to  electrical  properties;  or 
(f)  to  cryoscopic  behavior. 

Graham,"  in  his  classic  researches  on  diffusion,  studied  in- 
cidentally the  diffusion  of  a  few  double  salts,  among  them 
alum  and  the  double  sulphate  of^magnesium  and  potash.  He 
found  that  the  constituents  of  the  former  were  present  in  the 
diffused  1:  in  a  proportion  different  from  that  in  the  alum 

itself,  and  inferred  that  the  alum  in  solution  was  at  1  -  st  par- 
•tiall-  .omposed.  With  regard  to  the  latter  salt,  ht  *ound 
that  the  amount  of  the  double  salt  which  diffused  was  equal 
to  the  sum  of  the  amounts  diffused  of  its  constituents  taken 
separately  :  and  he  concluded  that  this  double  salt  was  not 
decomposed  in  solution.  As  Graham  had  not  determined  the 
proportions  in  which  the  constituents  of  the  double  sulphate 
of  magnesium  and  potash  had  diffused,  but  only  the  total 
amount  of  diffusion,  his  work  was  repeated  by  Marignac,' 

1  Phil.  Trans.,  1850,  i.  »  Aun.  cbira.  phys.,  [5],  a,  546.  (i374). 


who  concludficl  from  an  extensive  series  of  observations  that 
there  is  no  difference  between  mixtures  of  'alts  capable  of 
forming  double  salts  and  those  in  which  no  union  can  take 
place.     He  inferred  that  dou])le  salts  are  only  formed  at  the 
i.ioment  of  crystallization.     The  work  of  van  der  V.'al.'   who 
diffused  alums  atu'  other  double  sulphates,  and  of  Ingenhoes,' 
who  investigated  barium  acetonitrate  and  similar  salts,  lead 
to  the  same  result.     The  latter  found  that  the  constituents  of 
the  salts  examined  diffused,   not  in  the  proportion  in  which 
they  exist  in  the  double  salt,  but  nearly  as  if  diffused  sepa- 
rately,    kiidorff,'  following  the  same  mode  of  investigation, 
divided  double  sn.lts  into  two  classes,  according  as  their  con- 
stituents were  found  in  the  diffusate  in  the  same  proportion  as 
in  the  double  salt  or  in  a  different  proportion.     Riidorff  also 
investigated  the  relation  between  dissociation  and  concentra- 
tion and  found  that,  until  near  the  point  of  saturation,  the 
'two  were  independent ;  but  that  if  crystals  of  the  double  salt 
were  placed  upon  the  diaphragm  so  as  to  maintain  saturation, 
the  proportion  of  the  constituents  diffused  much  more  nearly 
approached  their  proportion  in  the  double  salt.     He  inferred 
that  molecular  compounds  exist  in  fully  saturated  solutions. 
This  inference  was  criticised  by  Ostwald,'  and  later  by  Tre- 
vor." on  the  ground  that  the  effect  observed  was  due  to  the 
more  rapidly  diffusing  constituent  becoming  relatively  less 
concentrated  in  the  diffusion  vessel  ;  and  the  latter  undertook 
a  series  of  experiments  confirming  this  view.     On  the  other 
hand,   E.   Fischer  and  Schmidner,'  by  allowing  a  saturated 
solution  of  ferrous  ammonium  sulphate  to  diffuse  upwards 
through  rolls  of  filter  paper  inside  a  glass  tube,  found  the 
proportion  of  the  constituents  in  the  filter  paper  the  same  as 
in  the  double  salt. 

In  the  field  of  thermochemistry,  conclusions  as  to  the  ex- 
istence of  double  salts  in  solution  are  based  upon  a  principle 
stated  by  Berthelot'  as  follows  :  "  Everything  indicates  that 
double  salts  formed  with  a  feeble  disengagement  of  heat  are 
to  be  regarded  as  separated  in  greater  part  into  their  constitu- 

1  Iiiaujrnral  Dissortatiovi.    Leyden,  (1869).       2  Ber.  d.  chem.  Ges.,  la,  1678,  (1879). 
»  Uer  d.  chem.  Ges.,  ai,  4 ;  3i.  1S82  ;  ai,  3044.  (1888) ;  33.  1846,  (1890). 
4  Ztsrhv.  phys.  Chem.,  3,  60:,  (18S9).  &  Ztschr.  phys.  Chem.,  7,  468,  (1891). 

«  Ann.  .  'i.-m.  (Uebig),  a?*.  156.  (1892)-  '  M^c.  Chem.,  II,  324- 


jscrvatlotis  that 
-alts  capable  of 
utiion  can  take 
y  formed  at  the 

der  Wal.'   who 
d  of  Ingenhoes,' 
iiilar  salts,  lead 
e  constituents  of 
portion  in  which 
if  diffused  sepa- 
jf  investigation, 
ng  as  their  con- 
nie  proportion  as 
ti.     Riidorff  also 
1  and  concentra- 
f  saturation,  the 
f  the  double  salt 
ntain  saturation, 
uch  more  nearly 
lit.     He  inferred 
irated  solutions, 
itid  later  by  Tre- 
l  was  due  to  the 
ig  relatively  less 
;  latter  undertook 
V.     On  the  other 
wing  a  saturated 

diffuse  upwards 
,  tube,  found  the 
iper  the  same  as 

ons  as  to  the  ex- 
upon  a  principle 
[ig  indicates  that 
ement  of  heat  are 
nto  their  constitu- 

etn.  Ges.,  la,  1678,  (1879). 
1846, (1890). 

lys.  Chem.,  7,468,  (1891). 
a.,  11,324- 


ents  by  water."  On  this  principle  Havre  and  Valson,'  find- 
ing that  the  constituents  of  the  alums  evolved  no  heat  oh 
mixing,  concluded  that  the  latter  come  into  existence  only 
throu^'h  crystallization.  Graham'  had  previou.sly  made  simi- 
lar experiments  with  other  double  sulphates,  reaching  the 
same  results.  Graham^  found,  on  the  other  hand,  that  ther- 
mal changes  occurred  when  solutions  of  the  chlorides  of  mer- 
cury and  ammonium  were  mixed.  vSimilarly,  Berthelot* 
found  that  in  general  the  thermal  changes  on  mixing  solu- 
tions of  the  halogen  salts  of  mercury  and  potassium  were  not 
equal  to  the  sum  of  the  thermal  changes  for  the  component 
salts,  and  concluded  that  the  existence  of  double  salts  in  such 
solutions  was  thereby  proved. 

Of  importance  in  their  bearing  upon  the  question  are  also 
the  volume  changes  which  occur  when  salt  .solutions  are 
mixed.  Kremers,'  finding  no  change  of  volume  on  mixing 
solutions  of  salts  capable  of  forming  double  .salts,  inferred 
that  no  double  salts  existed  in  solution,  on  the  ground  that 
chemical  changes  are  known  to  be  accompanied  by  changes 
of  volume  frequently  large.  Favre  and  Valson*  drew  a  simi- 
lar conclusion  from  the  fact  that  the  density  of  a  solution  of 
potassium  cupric  sulphate  is  the  mean  of  the  densities  of  its 
constituents.  Gerlach,'  however,  noticed  a  slight  contraction 
of  volume  in  the  case  of  the  alums  on  mixing  solutions  of 
their  constituents,  which  became  more  marked  with  increas- 
ing concentration  ;  and  upon  this  and  other  grounds  he  in- 
clined to  the  belief  that  these  double  salts  exist  as  such  in 
their  solutions.  The  conclusions  of  Groshans^  from  observa- 
tions on  double  chlorides  and  sulphates  confirmed  those  of 
Kremers. 

Researches  upon  the  solubility  of  salt  mixtures,  especially 
upon  the  states  of  equilibrium  in  solution  when  two  salts 
capable  of  forming  a  double  salt  are  dissolved  together,  have 
contributed  largely  to  a  knowledge  of  the  state  of  double  salts 
in  solution.      Mulder'  drew  from  the  work  of  Kopp'"  and 


1  Compt.  rend.,  74,  1165.  (1872). 

■  Phil.  Mag.,  34,  401,  (1844). 

6  Pogg.  Ann.,  98,  58,  (1856). 

•»  Ztschr.  anal.  Chem.,  a8,  485.  (1889). 

«  Jahrsb.  Chem.,  1864,  92  ;  1866,  65. 


a  Phil.  Mag.,  jo,  539,  (1842). 

4  Ann.  chim.  phys.,  [5],  39, 198,  (1883). 

8  Compt.  rend.,  77,  907,  (1873). 

8  Des  Dissolutions  Aqueuses,  2-7. 

10  Ann.  chem.  (Uebig),  34,  260,  (1840). 


I 


others,  cxtciulccl  liy  researches  of  hisown,  the  conclusion  that 
well-defined  double  salts  exist  in  saturated  solutions  of  salt 
mixtures.  This  conclusion  was  founded  upon  the  observa- 
tion that  ill  such  solutions,  saturated  with  respect  to  each 
component,  the  salts  are  often  found  in  simple  molecular  pro- 
portions. Some  researches  of  Riidorff'  seemed  to  lead  to  a 
different  conclusion.  These,  however,  have  been  otherwise 
interpreted  by  Trevor.'  The  studies  in  equilibrium  of  Ditte' 
on  the  double  iodide  of  lead  and  potassium  (PbI,.K,I,.«H,/)). 
of  Roozeboom*  on  astrakanite,  of  Meyerhoffer,"  Vriens," 
vSchreinemaker,'  and  van  der  Heide"  have  led  to  the  {general 
result  that  there  are  certain  limits  of  temperature  outside  of 
which  double  salts  are  capable  of  existing  in  their  soh-tions. 

From  van't  Hoff's  extension  of  the  gas  laws  to  .solutions 
Nernst"  deduces  the  consequence  that  if  to  a  saturated  salt 
solution  a  solution  of  another  salt  having  a  coiumon  ion  be 
added,  the  solubility  of  the  former  salt  is  decreased  and  a 
■part  of  it  precipitated.  On  examining  certain  cases  in  which 
the  solubility  of  the  first  salt  is  increased  under  the  conditions 
stated,  Le  Blanc  and  Noyes'"  succeeded  in  showing  that  the 
apparent  exceptions  were  due  to  the  formation  of  double  salts 
in  solution.  To  the  same  cause  Rose"  attributed  those  cases 
in  which  a  salt  is  found  to  be  more  soluble  in  the  solution  of 
another  salt  than  in  water.  The  view  that  the  solution  of 
silver  chloride  in  ammonia  is  accompanied  by  the  formation 
of  a  double  salt  in  the  solution  has  been  confirmed  by  Bod- 
lander." 

The  application  of  electrolysis  to  a  study  of  the  state  of 
double  salts  in  solution  was  made  early  in  the  present  cen- 
tury by  Porret,"  who  found  that  when  potassium  ferrocyanide 
was  electrolyzed,  alkali  appeared  at  the  negative  pole,  while 
oxide  of  iron  and  prussic  acid  appeared  at  the  positive.  The 
work  of  Daniell  and  Miller"  on  the  same  salt,  extended  by  Hit- 

l  Fogg.  Ann.,  148,  558,  (i873).  '  ^<^-  "'• 

»  Ann.  chem.  phys.,  [5],  a4,  226  (18S1). 

4  Ztschr.  phys.  Cliem.,  a,  513.  (1888) ;    la,  35Q  (1893). 

6  Ztschr.  phys.  Chem.,  3.  336.  (1889).  "  Ztschr.  phys.  Chem.,  7.  194.  (1891)- 

7  Ztschr.  phys.  Chera.,  9,  57.  (1892)  ;  H.  289,  (1893). 

8  Ztschr.  phys.  Chem.,  la,  416,  (189.O.  »  Zts.:hr,  phys.  Chem.,  4,  372.  ('889). 
10  Ztschr.  phys.  Chem.,  6.  38.5.  (1890).           '»  Poge^  Ann..  8a,  545,  (1851). 

W  Ztschr.  phys.  Chem.,  9,  730,  (1892)-  "  Phil.  Trans.,  1814.  527. 

14  Pogg.  Ann.,  64,  18,  (1845). 


;  conclusion  that 
solutions  of  salt 
wn  the  obscrva- 

respect  to  each 
.'  molecular  pro- 
led  to  lead  to  a 

been   otherwise 
ibriuni  of  Ditte' 
bI,.KJ,.«H,/)), 
loffer,"    Vriens," 
d  to  the  general 
ature  outside  of 
their  solftions. 
iws  to  solutions 
a  saturated  salt 
I  coiunion  ion  be 
decreased  and  a 
n  cases  in  which 
ler  the  conditions 
lowing   that   the 
)n  of  double  salts 
buted  those  cases 
1  the  solution  of 
t  the  solution  of 
by  the  formation 
snfirmed  by  Bod- 

y  of  the  state  of 
the  present  cen- 
iium  ferrocyanide 
ative  pole,  while 
le  positive.  The 
extended  by  Hit- 


I.  Chera.,  7.  194.  (1891)- 

1.  Chem.,  4,  372,  (1889), 
8a,  545,  (1851). 
,  1814.  527. 


torf  to  many  other  double  salts,  lead  to  the  view  that  double 
salts  are  of  two  classes  :  ( 1 )  those  which  tlo  not  exist  as  such 
in  solution,  and  (2)  those  containing  a  metal  coml)iued  with 
a  complex  radical,  which  are  capable  of  existing  in  water 
solution  undecomposed.  In  the  nomenclature  of  Ostwald* 
the  latter  are  "complex  salts,"  the  term  "double  salt"  being 
applied  to  members  of  the  first  class  only.  To  the  complex 
salts  he  refers  potassium  ferrocyanide  and  analogous  salts;  to 
the  double  salts  he  refers  the  alums.  Retwecn  these  extreme 
types  various  degrees  of  dissociation  may  exist. 

Researches  upon  the  electrical   conductivity  of  double  salts 
and  salt  mixtures  are  numerous.     Of  chief  imi)ortance  in  the 
present  connection  are  those  of  Bouchotte'  and  Paalzow*  on 
sulphates  of  copper  and  zinc  in  common  solution  ;  of  vSvenson' 
on  alums,  of  Grotrian'  on  the  salt  K,CdI,,  of  Freund,'  Ben- 
der," Bouty,'  Arrhenius,"and  Chrouslchoff  and  I'ackhoff"  on 
mixtures  of  electrolytes  ;  of  Klein'"  on  mixtures  and  double 
salts:  of  Wershoven"  on  dilute  solutions  of  cadmium  salts; 
and  of  Kistiakowsky'*  on  dilute  solutionsof  "complex"  salts. 
The  results  of  these  investigations,  in  so  far  as  they  refer  to 
the  dissociation  of  double  salts,  agree  in  showing  that  with 
increasing  dilution,  many  double  salts  rapidly  approach  the 
condition  of  a  simple  mixture.     For  concentrated  .solutions, 
Klein,  who  compared   the   conductivities  of  salt   mixtures 
capable  of  forming  double  salts  with  that  of  those  whose  con- 
stituents were  without  mutual  chemical  action,  showed  that 
in  the  former  case  the  difference  between  the  conductivity  of 
the  mixture  and  the  mean  conductiviiy  of  its  constituents 
was  much  greater  than  in  the  latter  case  ;  and  he  inferred 
that  in  concentrated  solutions  there  is  only  partial  dissocia- 
tion.    For  complex    salts  Kistiakowsky  found  that  e\ en  in 
very  dilute  solutions  their  complex  ions  remained  undecom- 
posed.    The  conductivity  method  has  also  been  applied  by 

1  PogK.  Aim.,  106,  51.1,  (i8,s9)-  *  Ztschr.  phys.  Chem.,  3,  596.  (1889)- 

8  Compt.  rend.,  6a,  955.  (1S66).  *  Pogg.  Ann.,  136,  489.  (1H69). 
»  Beibl,  a,  46,  {187S).  »  Wied.  Ann  ,  18,  177.  ("883). 
^  Wied.  Ann.,  7,  44,  (i879).  '  Wied.  Ann.,  aa,  179,  (1884). 

9  Ann.  cliini.  phys.  [6],  3,  433.  (1884) :  14.  74.  (1888). 
><»  Biebl.,  9,  437,  (1885)  :  Wied.  Ann.,  30,  51,  (i>^87). 

11  Compt.  rend.,  108,  1162,  (1889).  W  Wied.  Ann.,  a?,  151,  (1886). 

>8  Ztschr.  phys.  Chem.,  s,  481,  (1890).  "  Ztschr.  phys.  Chem.,  6,  97.  (iS9o)- 


i^,m  milinffia 


lO 

Le  Blanc  and  Noyes,'  by  Bodliincler'  and  others  to  indicate 
the  existence  of  double  salts  in  the  respective  cases  studied. 

The  application  of  the  freezing-point  method  has  been 
especially  studied  by  Raoult.'  By  comparing  the  lovering 
given  by  double  salts  with  the  sum  of  the  lowerings  of  their 
constituents,  he  concluded  that  certain  double  sulphates,  in- 
cluding the  alums,  are  entirely  dissociated,  while  other  salts 
examined,  as  the  chlorides  of  mercury,  go  into  solution  with 
but  partial  decomposition. 

From  the  foregoing  summary  it  will  be  seen  that  the  classi- 
fication of  double  salts  into  two  groups  according  as  they  are 
wholly  or  but  partially  decomposed  by  water  is  well  estab- 
lished so  far  as  regards  dilute  solutions,  but  that  in  more  con- 
centrated solutions  the  evidence  is  not  sufficient  to  regard 
the  classification  as  final.  The  present  investigation  has  been 
undertaken  with  the  object  of  obtaining  such  further  data  as 
may  justify  more  definite  conclusions.  The  work  has  been 
confined  to  .some  alums  as  representatives  of  an  extreme  type 
of  dissociation,  and  to  one  member  of  the  dissociated  class  of 
double  chlorides.  The  results  reached  are  based  upon  a  com- 
parison of  the  electrical  conductivity  and  cryoscopic  behavior 
of  the  double  salts  with  that  of  their  constituent  salts,  with  a 
view  to  determining  to  what  extent  the  solutions  of  the  double 
salts  correspond  to  mixtures. 

CotidticHvity  Apparatus. 
The  measurements  of  conductivity  were  made  by  the 
Kohlrausch  method,  using  a  Wheatstoue  bridge,  induction 
coil  and  telephone.  The  special  form  of  the  apparatus  used 
was  that  described  by  Ostwald."  The  bridge  wire  was  cali- 
brated by  the  method  of  Strouhal  and  Barus.'  Conduc- 
tivity cells  of  the  Arrhenius  form  were  employed  with  elec- 
trodes at  different  distances,  one  for  solutions  less  than  o.ooi 
normal,  the  other  for  those  more  dilute.  In  this  way  satis- 
factory tone  minima  were  obtained  throughout  a  wide  range 
of  dilution.  The  temperature  selected  for  the  measurements 
wa3,  in  general,  25°.     By  means  of  a  thermostat  the  tempera- 

1  Loc.  cit.  *  f'O':-  "i- 

8  compt.  rend.,  99,  gM.  OWH)-  *  Ztschr.  phys.  Chem.,  a.  561.  (1888). 

B  Wied.  Ann.,  10,  ii6,  (1880). 


others  1o  indicate 
s  cases  studied, 
nethod  has  been 
ing  the  lovering 
)\verings  of  their 
)le  sulphates,  in- 
while  other  salts 
iito  solution  with 

en  that  the  classi- 
rding  as  they  are 
ter  is  well  estab- 
that  in  more  con- 
fficient  to  regard 
stigation  has  been 
h  further  data  as 
le  work  has  been 
[  an  extreme  type 
issociated  class  of 
based  upon  a  com- 
yoscopic  behavior 
uent  salts,  with  a 
tious  of  the  double 


?re  made  by  the 
bridge,  induction 
le  apparatus  used 
Ige  wire  was  cali- 
Barus.'  Conduc- 
iployed  with  elec- 
)ns  less  than  o.ooi 
In  this  way  satis- 
hout  a  wide  range 
the  measurements 
lostat  the  tempera- 

s.  Chem.,  a,  561.  (1888). 


II 


ture  was  easily  kept  constant  under  ordinary  conditions  to 
within  o.  i  degree. 

Solutions. 
The  flasks  and  pipettes  used  in  making  up  solutions  were 
calibrated  for  a  temperature  of  20°,  the  former  by  the  ap- 
paratus devised  by  Professor  Morse  of  this  laboratory  and 
Blalock,'  the  latter  by  weighing  in  successive  portions  the 
water  delivered  at  a  known  temperature. 

The  solutions  were  prepared  at  20°  and  standardized  by 
analysis  of  a  measured  volume  except  in  the  few  cases  in 
which  the  concentration  could  be  known  from  the  weight  of 
the  salt  dissolved. 

As  the  character  of  the  water  effects  appreciably  the  con- 
ductivity of  solutions  more  dilute  than  0.02  normal,  the  water 
used  was  prepared  by  redistilling  ordinary  di.stilled  water 
successively  from  solutions  of  alkaline  and  acid  permanganate 
of  potash,  employing  a  block  tin  condenser.  The  water  so 
prepared  gave,  in  general,  a  conductivity  at  25°  varying  from 
1.5  to  2  X  io"°  mercury  units.  The  conductivity  of  the  water 
used  was  measured  for  each  series  of  determinations,  and  tne 
correction  applied. 

Conductivity  Measurement, 
In  making  a  series  of  conductivity  measurements  the 
general  method  adopted  was  to  make  up  from  the  original 
solution,  standardized  by  analysis,  a  .solution  which  was  a 
simple  multiple  or  fraction  of  normal  ;  25  or  50  cc.  of  this 
solution  were  then  measured  with  a  pipette  into  the  cell  and 
successive  solutions  prepared  from  this  in  the  cell  itself  by 
withdrawal  of  a  measured  portion  and  addition  of  an  equal 
volume  of  water.  As  a  check  upon  errors  of  dilution,  a  series 
of  solutions  were  made  up  independently  in  measuring  flasks 
at  intervals  corresponding  to  four  or  more  dilutions  in  the  cell. 
These  solutions  were  used  as  standards,  and  when  the  conduc- 
tivity of  the  cell  dilution  differed  a  proportional  correction 
was  applied,  in  the  manner  indicated  by  Kohlrausch,''  to  the 
members  of  the  series  immediately  preceding,  provided  this 
correction  did  not  exceed  0.5  or  0.75  per  cent ;  when  it  did, 

Am.  Chem.  J.,  l6,  479.  (1894).  *  Wied  Ann.  ,  a6.  1S4,  (1885). 


M>.      utmmsmaK^^ 


"Hfc 


13 


the  measurements  were  repeated.     The  cell  was  standardized 
at  frequent  intervals  with  0.02  normal  potassium  chloride. 

Certain  cases  occurred  in  which  the  solutions  were  found  to 
be  unstable  at  great  dilutions.  In  these  cases  the  check  solu- 
tions were  made  up  immediately  before  measuring  their  con- 
ductivity. 

A  Method  of  Titrating  Alunmiiufn. 
As  the  necessity  of  standardizing  solutions  containing 
aluminium  often  occurred  in  the  progress  of  the  work,  a  reliable 
and  convenient  method  of  titration  became  desirable.  None 
of  the  methods  described  in  the  literature  seem  to  have  proved 
satisfactory.  That  of  Bayer'  by  titration  of  sodium  aluminate 
with  sulphuric  acid,  using  litmus  and  methyl  orange  as  indi- 
cators, is  described  as  a  "tedious,  hot  and  uncertain  pro- 
cess ;'"  while,  in  the  method  of  Lunge,'  the  ratio  of  the  acid 
.  consumed  to  the  aluminium  has  been  the  subject  of  much  dis- 
cussion. 

After  some  unsuccessful  attempts  with  barium  hydroxide, 
the  following  method  of  titration  with  ammonia,  using  litmus 
as  an  indicator,  was  finally  adopted,  and  has  been  found  to 
give  fair  results  :  A  measured  volume  of  the  alum  solution  is 
heated  nearly  to  boiling,  and  the  sulphate  precipitated  with 
barium  chloride  avoiding  a  large  excess.     A  0.05    normal 
solution  of  ammonia  is  now  added  slowly  and  with  constant 
shaking   until   the   solution   reacts   weakly   alkaline.      The 
change  of  color  is  very  gradual  and  could  not  be  used  in 
direct  titration.      The  solution  is  now  diluted  to  a  known 
volume,  the  whole  operation  being  conducted  in  a  100  cc. 
flask,  and  allowed  to  stand  some  hours,  until  most  of  the  pre- 
cipitate has  settled.     Some  of  the  solution  is  then  decanted 
off  and  passed  through  a  small  filter,  the  first  part  of  the  filtrate 
being  thrown  away  to  avoid  change  in  concentration.     50  cc. 
of  the  filtrate  are  next  measured  off,  a  few  drops  of  litmus 
again  added  and  the  solution  titrated  to  color  with  standard 
hydrochloric  acid. 

A  solution  of  potassium  alum  titrated  in  this  way  gave  the 

following  results : 

I  Ztschr.  anal.  Chem.,  34.  54J,  (-SRs)-    »  K  B.,  Ztschr.  anal.  Chem.,  as.  '83-  («»86). 
8  Ztschr.  angew.  Chem.,  aa?,  ags.  ('890)- 


•SHN* 


'as  standardized 
uni  chloride, 
tiswere  found  to 
5  the  check  solu- 
uring  their  cou- 

ions  containing 
e  work,  a  reliable 
[esirable.  None 
n  to  have  proved 
odium  aluniinate 
1  orange  as  indi- 
d  uncertain  pro- 
ratio  of  the  acid 
aject  of  muchdis- 

iriura  hydroxide, 
nia,  using  litmus 
as  been  found  to 

alum  solution  is 
precipitated  with 

A  0.05  normal 
nd  with  constant 

alkaline.  The 
i  not  be  used  in 
uted  to  a  known 
:ted  in  a  100  cc. 
il  most  of  the  pre- 

is  then  decanted 
part  of  the  filtrate 
entration.  50  cc. 
r  drops  of  litmus 
lor  with  standard 

this  way  gave  the 

al.  Chem.,  asi  183.  (i»86). 
10). 


13 

I.   I  cc.  solution  contains  0.0948  gram  alum. 
II.   I  cc.        "  "  0.0946      " 

III.  I  cc.        "  "         0.0945      " 

IV.  I  cc.        "  "  0.0944      " 
V.   ICC.        "             "          0.0944      " 


Mean,  0.0945      "        " 
The  results  of  a  gravimetric  analysis  by  precipitation  of  the 
sulphate  with  barium  chloride  gave  0.09486  gram  alum  per  cc. 

I. 
Alums. 
Double  sulphates  conform  to  one  of  two  types  : 

I.  R',  SO,.  R"SO,  +  6H,0. 

II.  R',  SO,.  R'",  (SO,),+  24H,0. 

The   alums,    representing   the   latter  type,  form   a   group 
whose  members  are  united  by  the  closest  analogies.  Although 
taken  by  Rose'  as  the  chief  representives  of  a  class  of  double 
salts  not  easily  decomposed  by  water,  since  he   found  that 
repeated  crystallizations  gave  rise  to  no  decomposition,  later 
investigators,  as  Ostwald  and  Raoult,  regard  them  as  types 
of  extreme  dissociation.     Any  conclusions  reached,  therefore, 
with  regard  to  the  alums  from  this  point  of  view  become  im- 
mediately applicable  to  a  large  group  of  double  salts. 
Conductivity  Results. 
As  no  conductivity  data  at  25°  for  sufficiently  concentrated 
solutions  of  the  constituents  of  the  alums  were    available, 
measurements  were  made  for  potassium  sulphate,  aluminium 
sulphate  and  chromium  sulphate. 

Potassium  Sulphate. 
The  salt,  purified  by  repeated  crystallizations,  was  dried  to 
constant  weight  in  an  air-bath,  and  solutions  made  up  from  a 
weighed  amount  of  the  dry  salt. 

In  the  following  tables  conductivities  are  expressed  in 
"  molecular  conductivity"  units  as  defined  by  Ostwald, ^^  in- 
stead of  in  "equivalent  molecular"  units,  in  order  to  facilitate 
the  comparison  of  the  conductivities  of  solutions  containing 


I  Pogg.  Anu.,  8a,  545.  (1851). 


2  tehrbuch  der  allg.  Chem.,  a,  621. 


.! ; 


f  i 


14 

equal  numbers  of  gram-molecules  per  litre  but  of  different 
concentration  expressed  as  normal. 

The  symbols,  /i„i5°.  >".25^  denote  respectively  the  molecular 
conductivities  at  15°  and  25°,  the  numbers  in  the  columns 
being  multiplied  by  10'. 

The  only  direct  measurements  at  25°  available  tor  compari- 
son are  those  of  Walden,'  which  give  by  interpolation  a  very 
satisfactory  agreement.     Walden's  results  are  as  follows  : 


Litres  per 
gram-molecule. 

64.0 

128.0 

256.0 

512.0 

1024.0 

2048.0 


/^i,25  . 
232.2 
246.0 
256.8 
265.4 
272.8 
278.6 


K,SO.    [I7434]- 


Gram-molecules 
per  litre. 

0.333 

0.25 

0.2175 

0.10855 

O.I 

0.05427 

0.05 

0.0333 

0.025 

0.01666 

0.005 

0.0025 

0.0005 

0.00025 

0.00005 


Litres  per 
gram-molecule. 

0.3 
4.0 

4.6052 

9.2104 

10. 0 

18.4208 

20.0 

30.0 

40.0 

60.0 

200.0 

400.0 

2000.0 

4000.0 

20,000.0 


/^«/i5 


134-7 


148.2 

■  •  •  • 

162.9 
167.2 
171. 7 
179.4 
200.7 


/^z>25    . 

157-4 
167.9 
170.2 
186.9 
187.0 
202.8 
205.1 
213.9 
220.3 
229.1 

252.4 
262.2 
276.5 
281.9 
279.6 


237-8 

Aluminium  Sulphate. 
The  ordinary  chemically  pure  aluminium  sulphate  was 
found  to  contain  considerable  quantities  of  sodium.  The 
aluminium  sulphate  used  was  prepared  from  pure  potassium 
alum.  The  aluminium  was  precipitated  as  hydroxide  by  am- 
monia, and  the  precipitate  washed  until  it  was  found  to  be 
entirely  free  from  potassium  and  ammonia.  The  washing 
was  effected  by  boiling  the  precipitate  with  large  quantities 

1  Ztschr.  phys.  Chem.,  3,  49.  (i88S). 


;  but  of  different 

:ely  the  molecular 
;  in  the  columns 

lable  for  compari- 
terpolation  a  very 
ire  as  follows  : 

^25°. 

132.2 
!46.o 
J56.8 

!65.4 
272.8 
278.6 


/^f25   . 

157-4 

167.9 

170.2 

186.9 

187.0 

202.8 

205.1 

213.9 

220.3 

229.1 

252.4 

262.2 

276.5 

281.9 

279.6 


lium  sulphate  was 
of  sodium.  The 
)m  pure  potassium 
s  hydroxide  by  am- 
it  was  found  to  be 
nia.  The  washing 
th  large  quantities 

888). 


15 

of  water,  allowing  it  to  settle  and  successively  decanting  and 
filtering.  This  treatment  was  repeated  a  dozen  or  fifteen 
times.  The  pure  aluminium  hydroxide  was  dissolved  in  sul- 
phuric acid  in  slight  excess,  as  indicated  by  methyl  orange, 
and  the  excess  of  acid  removed  by  repeated  precipitation  of 
the  salt  with  alcohol,  the  last  traces  of  alcohol  being  re- 
moved by  heating  in  an  air-bath.  The  salt  so  obtained  was 
in  the  form  of  a  light  powder  and  answered  every  test  of 
purity.     Analysis  gave  the  following  resuls  : 

Calculated  for 
A1,(S04),. 

Al        0.0479 
SO,      0.2548 

Analysis  of  the  standard  solution  gave  : 

I.  0.044706  gram  A1,(S0J,  per  cc. 

II.  0.044778  gram  A1,(S0,),  per  cc. 

Mean,   0.04474    gram    A1,(S0,).   per  cc,   equivalent    to 
0.1307  gram-molecules  per  litre. 


Found. 
0.048 
0.255 


A1,(S0J.  [342.34]- 


Oram- 

moleciiles 

per  litre. 

O.21715 

0.10855 

0.06666 

0.05427 

0.03333 

0.016666 

0.003333 

0.001666 

0.0005 

0.0003333 

0.00025 

0.0001666 

0.00003333 

0.000025 

0.0000166 

0.0000125 

0.00000625 


ivitres 
per  gram- 
molecule. 

4.6052 

9.210 

15.0 

18.4208 

30.0 

60.0 

300.0 

600.0 

1999.9 

3000.0 

3999-9 

6000.0 
30000.0 
40000.0 
60000.0 
80000  o 
160000.0 


;^i-i5  - 

•  •  •  • 

107.7 

•  •  •  • 

•  •  •  • 

139.1 

•  •  •  • 

243.6 

•  •  •  • 

382.4 

•  •  •  • 

447-4 

«  «  •  • 

•  •  •   • 

678.4 

•  •  •  • 

708.7 
715.2 


1. 

105.7 
130.3 
148.2 

153-6 

172.5 
202.3 

300.4 
359-5 


II. 

O 

/^x/25    ■        Mean. 


148.5    148-3 


172.7 
202.1 
300.8 
358.6 


172.6 
202.2 
300.6 
359.0 


530.0      531-7    530.8 


611.6 
806.1 


511.4 
809.1 


611. 5 
807.6 


869.4      869.4   869.4 


i6 

These  results  for  aluminium  sulphate  show  a  good  agree- 
ment with  Walden's  measurements  of  dilute  solutions  at  the 
same  temperature. 

Chromium  Sulphate. 

The  chromium  sulphate  used  was  a  specimen  prepared 
under  the  direction  of  Professor  Renouf  of  this  laboratory. 
The  process  consisted  in  the  reduction  of  chromic  acid  with 
ether  under  a  bell-jar,  filtration  of  the  solidified  crystalline 
mass  with  the  aid  of  a  pump,  and  careful  drying  of  the  prod- 
uct on  plates  of  unglazed  porcelain.' 

A  concentrated  solution  of  the  salt  was  prepared.  To 
diminish  errors  of  analysis,  the  solution  standardized  was  pre- 
pared from  the  original  by  diluting  one  volume  to  twenty. 
Analysis  gave  : 

I.  0.007426  gram  Cr,(SO,),  per  cc. 

II.  0.007410  gram  Cr,(S0,)5  per  cc. 
Mean,  0.007418  gram  Cr,j(vSOJ,  per  cc. 

Hence  the  original  solution  contained  0.3779  gram-mole- 
cules per  litre. 

The  conductivity  values  obtained  by  Walden"  differ  widely 
from  those  in  the  following  table  for  the  conductivity  of  chro- 
mium sulphate.  A  comparison  of  a  few  approximately  cor- 
responding dilutions  will  show  the  extent  of  the  difference. 
Column  I  gives  Walden's  values  reduced  to  molecular  con- 
ductivity units ;  column  2,  those  from  the  following  table  for 
chromium  sulphate  at  the  same  temperature  : 


Column  2. 

;Uj,  25'' =  288.2  (1"=     200) 
346.5  {v=^    400) 

558.2    (j/=  2000) 


Column  I. 

A*.'25°=  378.0  {v=  192) 
439.2  {v=  384) 
589.2  {v=  1536) 
669.6  {v  •=  3072) 

If  the  mean  be  taken  of  the  conductivity  values  obtained 
by  Walden  for  chromium  sulphate  and  those  corresponding  for 
potassium  sulphate,  it  leads  to  values  for  the  conductivity  of 
potassium  chrome  alum  greatly  in  excess  of  those  obtained  in 
the  present  investigation. 

The  conductivity  measurements  for  chromium  sulphate  are 
shown  in  the  lollowing  table  : 

I  Renouf:  Inorganic  Prep.,  p.  78.  2  Ztschr.  phys.  Chem.,  1,  541,  (1887). 


£ 


a  good  agree- 
slutions  at  the 


imen  prepared 
his  laboratory, 
amic  acid  with 
fied  crystalline 
ig  of  the  prod- 
prepared.  To 
irdized  was  pre- 
mie to  twenty. 


'79  gram-tnole- 

:n°  differ  widely 
ictivity  of  chro- 
roximately  cor- 

the  difference. 

molecular  con- 
owing  table  for 

iluran  2. 

88.2    (V=     200) 

46.5  iv=    400) 

58.2   (V  =  2CXK)) 

iralues  obtained 
)rresponding  for 
conductivity  of 
hose  obtained  in 

iim  sulphate  are 

lem.,  I,  S4i>  (1887). 


17 

Cr,(SO,).  [392.58]. 


Gram-moltcules 

Litres  per 

_ 

. 

per  litre. 

Kraiii-molecule. 

A'fi5  • 

A'j'25 

0.333 

30 

•  •  •  • 

94.2 

0.25 

4.0 

86.2 

107.3 

O.I 

10.0 

•  •  •  • 

139.0 

0.05 

20.0 

132.3 

162.7 

0.025 

40.0 

•  •  •  « 

190.7 

0.005 

200.0 

233-2 

28S.2 

0.0025 

400.0 

•  •  •  • 

346.5 

0.0005 

2000.0 

•  •  •  • 

558.2 

0.00025 

4000.0 

•   •  •  • 

671.2 

Potassium  Aluminium  Alum. 

The  salt  was  purified  by  repeated  crystallizations,  and  was 
found  to  be  free  from  iron,  sodium  and  ammonia.  A  solution 
was  prepared  approximately  saturated  at  20°.  The  solution 
was  standardized  by  precipitation  of  the  sulphuric  acid  with 
barium  chloride.     The  results  of  analysis  were  : 

I.  0.0952  gram  KA1(S0,),-|-  12  H,0  per  cc. 

II.  0.0948  gram  KA1(S0,),+  i2H,0  per  cc. 

III.  0.09458  gram  KAKSOJ,  +  i2H,0  per  cc. 

Mean,  0.09486  gram  KA1(S0,),-|-  i2H,0  per  cc.  of  solu- 
tion, or  equivalent  to  0.19995  gram-molecules  per  litre. 
The  conductivity  obtained  is  shown  in  the  following  table  : 

KAl(SO.),-f  i2H,0  [4744I]. 


Grnm- 

Litres  per 

L 

u. 

molecules 

:'ram- 

0 

n 

per  litre. 

molecule. 

/^z'25   . 

;'r.25   . 

Mean 

0.19995 

5.0012 

133-9 

133.9 

133-9 

0.125 

8.0 

149.2 

149.2 

149.2 

0.05 

20.0 

178.3 

178.3 

178.3 

0.025 

40.0 

202.5 

202.5 

202.5 

0.005 

200.0 

268.2 

269.9 

269.0 

0.0025 

400.0 

304.2 

306.3 

305.2 

0.0005 

2000.0 

407.0 

406.8 

406.9 

0.00025 

4000.0 

468.2 

466.8 

467-5 

Sodium  Aluminium  Alum. 

The  alum  was  made  to  crystallize  from  a  water  solution  of 
its  constituents  by  pouring  a  layer  of  alcohol  upon  the  surface 
of  the  solution.  With  the  gradual  diffusion  of  the  alcohol 
large,  well-formed  crystals  of  soda-alum,  together  with  a  few 


f.  ! 


u 


i8 

crystals  of  sodium  sulphate  appeared.  When  the  mixture 
was  washed  quickly  with  cold  water  the  small  crystals  of  so- 
dium sulphate  dissolved,  leaving  the  alum  perfectly  homo- 
geneous throughout.     Analysis  of  a  standard  solution  gave  : 

[.  0.02402  gram  NaAl(SO,),-h  i2H,0  per  cc. 

II.  0.02407  gram  NaAl(SO.),+  i2H,0  per  cc. 

Mean,  0.024047  gram  alum  per  cc.  equivalent  to  0.05247 
gram-molecules  per  litre. 

Conductivity  results  are  shown  in  the  following  table  : 

NaAl(SO.),-hi2H,0  [458.33]- 


Oram- 

molfcules 

per  litre. 

0.05 

0.025 

0.005 

0.0025 

P.OOO5 

0.00025 


Ulres  per 

Kr.-\m- 
molecule. 

20.0 

40.0 

200.0 

400.0 

2000.0 

4000.0 


I. 

161.5 
184.4 
250.0 
286.7 
380.0 

435-5 


II. 
;^^25°. 
161.6 
184.7 
251.2 
284.2 
378.8 
435-2 


Mean. 
161.6 
184.6 
250.6 
285.4 

379-5 
435-5 


Ammonium  Aluminium  Alum. 


After  eleven  crystallizations  the  salt  was  found  to  be  free 
from  sodium,  but  still  retained  a  minute  trace  of  potassium. 
The  standard  solution  was  analyzed  by  titration  of  the  alumin- 
ium.    The  analysis  gave  the  following  results  : 

I.  0.04550  gram  (NH,)A1(S0J,+  i2H,0  per  cc. 

II.  0.04585  gram  (NH,)AUSO,),+  I2H,0  per  cc. 
Mean,  0.04567  gram  alum  per  cc,  equivalent  to  0.10076 

gram-molecules  per  litre. 

(NHJAl(SOJ,  +  i2H,0  [453-19]- 
I.  n. 

152.8 

174-5 
198. 1 

261.4 

297.1 
390.0 

452.4 
568.4 

608.4 


Gram- 
molecules 
per  litre. 

O.I 

0.05 

0.025 

0.005 

0.0025 

0.0005 

o  00025 

0.00005 
0.000025 


Utres  per 

gram- 
molecule. 

10. 0 

20.0 

40.0 

200.0 

400.0 

2000.0 

4000.0 

20000.0 

40000.0 


152-9 

175-0 
198.4 
260.6 

294-9 
389.2 

452.4 
560.0 
602.8 


M  ean. 
152.8 
174.8 
198.2 
261.0 
296.0 
389-6 
452.4 
564.2 
605.6 


the  mixture 
rystals  of  so- 
rfectly  homo- 
alution  gave  : 

;c. 

nt  to  0.05247 

tig  table  : 


Mean. 
161.6 
184.6 
250.6 
285-4 

379-5 
435-5 


and  to  be  free 

of  potassium. 

.  of  the  ahirain- 

>er  cc. 

per  cc. 

ent  to  0.10076 


9]. 


- 

M  ean. 

9 
0 

4 
6 

152.8 
174.8 
198.2 
261.0 

9 
2 

296.0 
389-6 

4 
0 

8 

452-4 
564.2 
605.6 

19 

Potassium  Chrome  Alum. 

The  salt,  purified  by  repeated  crystallization  from  water  at 
35°,  was  dissolved  and  the  solution  standardized  by  precipi- 
tation of  the  sulphuric  acid  as  barium  sulphate.  The  analy- 
sis gave : 

I.  0.11742  gram  KCr(SO,),  +  i2H,0  per  cc. 

II.  o.ii746gram  KCr(SO,),-f-  i2H,0  per  cc. 

Mean,  0.1 1 744  gram  chrome  alum  per  cc,  equivalent  to 
0.2351  gram-molecules  per  litre. 

Following  are  the  results  of  conductivity  measurements  : 

KCr(S0J,-j-i2H,0  [499-53]. 


Gram- 
molecules 
per  litre. 

Litres  per 

gram- 
molecule. 

O.I 

TO.O 

0.05 

20.0 

0.025 

40.0 

0.005 

200.0 

0.0025 

400.0 

0.0005 

2000.0 

0.00025 

4000.0 

I. 

II. 

/^.25°. 

A'„25°. 

Mean. 

147.8 
170-5 

195-4 
266.7 

148. 1 

170.3 
195.0 
266.5 

147-9 
170.4 

195-2 
266.6 

306.1 
418.6 
472.4 

304-9 
418.8 
471.6 

305-5 
418.7 
472.0 

Ammonium  Chrome  Alum. 

The  salt  was  purified  as  in  the  case  of  the  potassium  chrome 
alum,  and  the  solution  standardized  by  precipitation  of  the 
sulphate.     The  analysis  gave  : 

I.  0.09266  gram  (NH.)Cr(SO,),  -|-  i2H,0  per  cc. 

II.  0.09282  gram  (NHJCr(SO,),  +  i2H,0  per  cc. 
Mean,  0.09274  gram  alum  per  cc,  equivalent  to  0.194  gram- 
molecules  per  litre. 

The  conductivity  observed  is  shown  in  the  following  talile  : 

(NHJCr(SO,),+  i2H,0  [478.44]- 


Gram- 
molecules 
per  litre. 

Litres  per 

grom- 
molecule. 

/'.25°- 

O.I 

10. 0 

145-4 

0.05 

20.0 

167.2 

0.025 

40.0 

I9I-5 

0.005 

200.0 

263.8 

0.0025 

400.0 

304.0 

0.0005 

2000.0 

.... 

0.00025 

4000.0 

484.6 

II. 

/Wri25°. 
144.7 
167. I 
191. 1 
263.6 
303-6 

4J5-3 
477-5 


Mean 
145.0 
167. 1 

I9I-3 
263.7 

303-8 

415-3 
481.0 


I     T" 


20 

Green  Modification  of  Ammonium  Chrome  Alum. 

As  is  well  known,  solutions  of  chrome  salts  at  a  tempera- 
ture between  70°  atul  80°  lose  their  original  color,  passing  to 
f.  green,  and  cease  to  have  the  power  of  depositing  crystals. 
Recoura'  has  shown  that  the  green  modification  is  a  well- 
defined  basic  salt  mixed  with  free  acid  ;  and  Monti'  has  found 
that  the  change  i  accomplished  by  a  rise  in  conductivity. 
With  a  view  to  fiiuling  whether  the  passage  to  the  green  modi- 
ficatior  is  discontinuous  at  any  point,  a  series  of  qualitative 
experiments  were  made  by  placing  the  conductivity  cell  con- 
taining a  solutii  n  of  ammonium  chrome  alum  in  a  bath, 
and  regulating  the  heat  so  that  the  temperature  rose  uni- 
formly with  t)io  time,  noting  at  the  same  time,  at  regular 
interval.*,  the  rise  in  conductivity.  The  latter  showed  no 
rapid  rate  o^  change,  and  it  may  be  inferred  that  the  pas- 
sage to  the  gieon  modification  is  a  continuous  change. 

Ammonium  Iron  Alum. 

A  solution  of  the  pure  alum  was  standardized  by  titration 
of  the  reduced  ferric  salt  with  potassium  permanganate,  the 
reduction  having  been  effected  by  a  platinum-zinc  couple. 
The  results  of  analysis  were  : 

I.  0.24772  gram  (NHJFe(SO,),  +  i2H,p  per  cc. 

II.  0.24722  gram  (NH,)Fe(SO,),  +  I2H,0  per  cc. 
Mean,o.2t747  (NH,)Fe(vSOj,  +  i2H,0percc.,  equivalent 

to  0.5080  gram-molecules  per  litre. 

Conductivity  results  are  shown  in  the  following  table  : 

UNH.)Fe(SO.),-f  i2H,0  [482.24]. 


Gram-m()!ecu!es 
per  litre. 

o,::5 
o  0.5 
o  025 
o.cx)5 


Litres  per 
gram-molecule. 

4.0 

20.0 

40.0 

200.0 


118. 9 
177.4 
211. 5 
320.2 


StibiUty  of  Alums  in  Dilute  Solutions. 
In  the  course  of  the  preceding  measurements,  it  was  noticed 
that  the  conductivities  of  dilute  solutions  of  some  of  the  alums 

»  Ann.  chim.  phys.,  [7].  4.  494.  (i«9.s)- 

a  Zlschr.  auorg.  CUem.,  la,  75.    Refer.,  (April,  1896.) 


|Ml)WtM<>Mpil|fcMagjMiSR^JI«'aW«».*^to--«-«'*":.Aiifa»-'a^w*--«^  - 


Alum. 

It  a  tempera- 
^r,  passing  to 
iting  crystals, 
on  is  a  well- 
)nti''  has  found 
conductivity, 
le  green  niodi- 
of  qualitative 
ivity  cell  con- 
ni  in  a  bath, 
ure  rose  uni- 
ne,  at  regular 
ter  showed  no 
that  the  pas- 
hange. 


d  by  titration 
anganate,  the 
n-zinc  couple. 

er  cc. 

per  cc. 

cc,  equivalent 

ng  table  : 

/'7'25°. 

118.9 
177.4 
211.5 
320.2 

,  it  was  noticed 
lie  of  the  alums 


2t 

incrca.scd  at  a  more  or  less  rapid  rate  on  standing  for  a  time. 
As  such  a  cliange  of  conductivity  must  depend  upon  changed 
conditions  in  the  solution,  this  observation  indicates  a  tliffer- 
ent  degree  of  stability  in  the  presence  of  a  large  amount  of 
water.  Ammonium  iron  alum  furnished  the  most  marked  iti- 
stance  of  instability.  At  a  dilution  of  200  litres  the  conduc- 
tivity of  a  solution  of  iron  alum  rose  3  per  cent,  in  two  hours. 
At  400  litres  it  showed  the  same  increase  in  twenty  minutes, 
and  at  a  dilution  of  2000  litres  the  rate  of  increase  was  about 
1.2  per  cent,  per  minute.  This  rate  soon  diminished  and,  at 
the  end  of  twenty-four  hours,  an  apparent  state  of  equilibrium 
was  reached  after  a  total  increase  in  conductivity  of  30  per 
cent.  At  o"  a  dilution  of  1000  litres  is  reached  before  decom- 
position begins.  The  precipitate  which  accompanies  the  de- 
composition does  not  become  visible  until  after  the  change  in 
conductivity  has  become  apparent.  A  rise  in  conductivity 
was  also  noticed  in  the  case  of  soda  alum  and  ammonium 
chrome  alum,  but  not  until  a  dilution  of  20,000  liters  was 
reached.  The  former  at  this  dilution  showed  an  increase  of 
4  per  cent,  in  twenty-four  hours.  Similar  examples  of  a  rise 
in  conductivity  in  dilute  solutions  have  been  noticed  by  Kohl- 
rausch'  in  the  case  of  barium  nitrate,  copper  sulphate  and 
other  salts.  In  the  former  case  it  was  clearly  accompanied  by 
the  formation  of  a  basic  salt,  and  the  liberation  of  free  acid. 
In  the  case  of  chromium  salts  the  rise  in  conductivity  accom- 
panying the  formation  of  a  basic  salt  has  already  been  men- 
tioned. The  well-known  tendency  of  ammonium  iron  alum 
to  form  basic  salts  is  doubtless  the  cause  of  the  change  of  con- 
ductivity noticed  in  its  case.  It  seems  probable,  therefore, 
that  a  similar  change  occurs  in  very  dilute  solutions  of  soda 
and  ammonium  chrome  alums  brought  about  by  the  action  of 
a  large  mass  of  water.  Such  a  change  would  be  analogous  to 
that  studied  by  Rose''  in  the  case  of  acid  potassium  sulphate, 
which  is  decomposed  by  an  excess  of  water  forming  the  neu- 
tral sulphate  and  free  acid. 

Comparison  of  Conductivity  Results. 

If  the  foregoing  conductivities  of  the  alums  be  compared, 


1  Wied.  Ann.,  a6, 175,  (1885). 


»  Pogg.  Ann.,  8a,  S45.  (•■851). 


it  will  be  seen  that  throu^jhout  all  dilutions  tlicy  can  be  ar- 
ranKcd  in  order  of  magnitude  with  respect  to  their  conductivi- 
ties from  a  knowled^;e  of  the  conductivities  of  their  constitu- 
ents. The  conductivities  of  potassium,  sodium  and  ammo- 
nium suli)hates  are  in  the  same  order  of  magnitude  as  the 
conductivities  of  the  cnrrespondinj;  alums. 

A  detailed  comparison  of  the  conductivities  of  the  alums 
with  the  arithmetic  means  of  the  conductivities  of  their  con- 
stituents is  shown  in  the  follov.inR  tables.  The  data  for  the 
values  of  conductivity  of  aluminium  sulphate  have  beeti  ile- 
rived  from  the  table  already  aWt-n,  supplemented  by  WaU 
den's'  results.  The  values  given  have  been  interpolated  by 
the  graphic  method.  The  data  for  sodium  sulphate  are  inter- 
polated from  Kohlrausch's'  tables  reduced  to  25"  and  changed 
to  molecular  conductivity  units.  The  values  for  potassium 
sulphate  and  chromium  sulphate  are  taken  directly  without 
interpolation  from  the  tables  already  given.  No  data  for  am- 
'nionium  sulphate  and  ferric  sulphate  are  available.  As  the 
latter  only  exists  in  acid  solution,  direct  observations  of  its 
conductivity  would  have  no  value  for  the  present  purpose. 


/.  Potassium  Aluminium  Alum. 


Litres 
molecule. 

KjSO,. 

AI,{SO,),. 
/'r25°. 

Alum,  observed 
Aritliinetic            ,,  „_o 
mtun.               f*v2^  , 

Difference. 
Per  cent. 

5.0012 

172.7 

108.0 

140.3                133.9 

—4.5 

8.0 

183.3 

124.2 

153.7                149.2 

—3.0 

20.0 

205.1 

158. 1 

181.6                178.3 

—  1.7 

40.0 

220.3 

185.7 

203.0               202.5 

— 0.2 

200.0 

252.4 

290.4 

271.4               269.0 

—0.8 

400.0 

262.2 

342.6 

302.4               305.2 

+0.9 

1  Ztschr.  phys.  Chem.,  i,  54i.  (i***?). 
a  Wicd.  Ann.,  a6,  iy6,  (18S5). 


i«M»ii'rii, 


ey  can  be  ar- 
icir  coiuluctivi- 
their  coiistitu 
im  and  anuno- 
piitiulc  as  the 

;  of  the  alums 
s  of  their  con- 
le  data  for  the 
have  beeti  ile- 
Mited  by  Wal- 
jiterpoUitcd  by 
phate  are  inter- 
'.^"  and  changed 
for  potassium 
irectly  without 
Mo  data  for  am- 
ilable.  As  the 
ervations  of  its 
2nt  purpose. 


observed. 
If25°. 

Difference. 
Per  cent. 

133-9 

—4-5 

149-2 

—30 

178.3 

—  1.7 

202.5 

— 0.2 

269.0 

—0.8 

J05.2 

+0.9 

//.  Sodium  ,Vnminiitlii  Alum, 


I.ilrFit 

per  writni- 
mol.cule 

20.0 

40.0 
200.0 
400.0 


No,HO«. 
A'r25°. 

171-5 
183-1 
211. 6 
219. 1 


i5«-i 

18.5-7 
290.4 

342-6 


mean. 
164,8 
184.4 
251.0 
280.8 


Alum.  AP^irrvcd. 
Mr25". 

I6I.6 
184.6 
750.6 
285.4 


Ulfferrnce, 
I'er  cent, 

—  1-9 
-1-0. 1 
—0.2 
+  1.6 


///,  Potassium  Chrome  Alum, 


Mtren 
per  Ktnitj- 
molecnle. 

K,SO,. 
/'r25°. 

Cr,(SO.),. 
^'.25°. 

Arithmetic 
mean. 

Alum,  observed 

;<^25^ 

Difference. 
I'er  cent. 

10. 0 

187.0 

139.0 

163.0 

147.9 

9.2 

30.0 

205.1 

162.7 

183.9 

170.4 

—7-3 

40.0 

220.3 

190.7 

205.5 

195-2 

—5.0 

200.0 

252.4 

288.2 

270.3 

266.6 

—1-3 

400.0 

262.2 

346.5 

304.3 

305-5 

+0.4 

aooo.o 

276.5 

558.2 

417-3 

418.7 

+0.3 

4000.0 

281.9 

671.2 

476.5 

472.0 

—0.9 

A  study  of  the  preceding  tables  justifies  the  following  state- 
ments : 

( I )  In  concentrated  solutions  the  conductivity  of  the  alums 
is  notably  less  than  the  mean  of  the  conductivities  of  their 
constituents.  (2)  The  defect  of  the  conductivity  from  the 
mean  is  the  same  in  amount  for  the  aluminium  alums,  while 
it  becomes  much  greater  for  chrome  alum,  (3)  The  differ- 
ence between  the  conductivity  of  the  alums  and  the  mean  con- 
ductivity of  their  constituents  grows  rapidly  less  with  increas- 
ing dilution,  so  that  at  a  dilution  of  40  litres  for  the  aluminium 
alums  and  of  400  for  chrome  alum  it  has  disappeared. 

Deductions  from  these  facts  must  depend  upon  the  relations 
which  exist  between  the  conductivity  of  a  mixture  of  two 
electrolytes  having  a  common  ion  and  the  conductivities  of 
the   constituents  taken   separately — assuming  that  the  state 


i    ! 


24 

of  the  alum  in  solution  is  the  same  as  if  it  had  been  formed 
by  mixing  equal  volumes  of  solutions  of  its  constituents  having 
the  same  molecular  concentration  as   itself.      It  has   been 
shown,  especially  by  the  work  of  Bender'  and  Klein",  that  in 
such  mixtures  the  conductivity  is  in  general  less  than  the 
mean   of  the  conductitivities  of  the  constituent  .^alts.     But 
Klein  showed  that  a  more  marked  difference  existed  when 
the  salts  were  capable  of  forming  a  double  salt.     Thus  while 
potassium  sulphate  and  sodium  sulphate  gave  a  difference  of 
I  per  cent.,  potassium  sulphate  with  ferrous  sulphate  gave  for 
the  same  concentration  6  per  cent.     The  differences  found  for 
the  alums  as  given  in  the  above  table  are  of  the  same  order 
(2U0  II  percent.)  as  those  found  by  Klein  for  the  double 
salts  examined  by  him. 

The  condition  that  two  electrolytes  having  a  common  ion 
may  mix  without  undergoing  a  change  in   ionization,  has 

.  been  deduced  from  the  dissociation  theory  of  electrolytic  con- 
duction by  Arrhenius.'  If  no  change  of  volume  occurs  on 
mixing,  that  condition  is  that  the  concentration  of  the  ions, 
i.  e.,  the  quotient  of  the  coefficient  of  ionization  divided  by 
the  volume  containing  one  gram-molecule,  shall  be  the  same 
for  the  both  solutions,  or 


where  «,,  «„  are  the  coefficients  of  ionization  of  the  respective 
solutions  ;  «,,  «,.the  number  of  gram-molecules  contained  re- 
spectively in  a  unit  of  volume  of  each;  and  z*,,  z\,  the  re- 
spective volumes  of  the  solutions  mixed. 

The  following  table  shows  the  extent  to  which  this  condi- 
tion is  fulfilled  in  some  of  the  solutions  of  alums  being  studied. 
On  the  assumption  already  made,  that  we  may  regard  a  solu- 
tion of  the  alum  as  having  been  formed  by  mixing  equal 
volumes  of  solutions  of  its  constituents  of  the  same  molecular 
concentration,  «,  and  «,  in  the  preceding  equation  become 
equal  as  also  z\  and  v,,  and  it  is  only  necessary  to  compare  the 
values  of  a,  and  ct„  for  the  constituent  solutions.  The 
values  of  a  have  been  calculated  from  freezing-point  data  in- 
stead of  from  conductivity,  since  the  experimental  error  in 
1  Loc.  at.  "^  ^-'"■-  "■'■ 

«  Ztschr.  phys.  Chera.,  a,  284,  (1888). 


< 


25 


[lad  been  formed 
nstituents  having 
f.  It  has  been 
id  Klein",  that  in 
;ral  less  than  the 
tuent  jalts.  But 
ce  existed  when 
salt.  Thus  while 
Lve  a  difference  of 
sulphate  gave  for 
ferences  found  for 
if  the  same  order 
n  for  the  double 

ng  a  common  ion 
n  ionization,  has 
)f  electrolytic  con- 
rolume  occurs  on 
ation  of  the  ions, 
zation  divided  by 
shall  be  the  same 


n  of  the  respective 
:ules  contained  re- 
and  z',,  ^',,  the   re- 

which  this  condi- 
ums  being  studied, 
may  regard  a  solu- 
.  by  mixing  equal 
he  same  molecular 
;  equation  become 
iary  to  compare  the 
t  solutions.  The 
zing-point  data  in- 
jerimental  error  in 

388). 


measuring  n^  for  aluminium  sulphate  and  chromium  sulphate 
may  become  very  large.  For  potassium  sulphate  the  two 
methods  give  concordant  results,  as  is  shown  in  the  table 
given  by  Arrhenius.'  In  calculating  the  valuesof  i,  thatis,  the 
ratio  between  the  observed  and  the  normal  osmotic  pressure, 
the  value  1.88  is  taken  for  normal  molecular-lowering.  The 
corresponding  values  of  a  are  calculated  from  the  equation 

?■=  /+  {k — /)  a. 
where  k  denotes  the  number  of  ions  given  by  each  active 
molecule,  namely,  3  for  potassium  sulphate  and  5  for  alumin- 
ium sulphate. 

AljCSOjj) 


Gram-molecules        K,SO, 

per  litre. 

i. 

a. 

0.117 

2.22 

o.6i 

o.ro86 

2.28 

0.64 

O.I 

2,30 

0.65 

0.098 

.... 

•   ■  •  • 

0.088 

2-33 

C.66 

0.0653 

•   •  •  • 

.... 

0.059 

2.41 

0.70 

0.054 

2-45 

0.72 

0.05 

2.44 

0.72 

0.0333 

2-57 

0.78 

0.0294 

2.57 

0.78 

0.026 

.... 

•   •  •  • 

Cr,(S04), 


a. 


2.13       0.28 


2.21 


2-34 


0.30 


2.44      0.38 


t. 
2.20 

•    •  ■  • 

2.21 

■    •  •  • 

2.28 
2.40 
2.44 
2.55 


n. 
0.30 

0.30 

•  •  •  * 

0.32 

•  •  •  • 

0-35 

•  •  •  • 

0.38 
0.387 


2.60      o  40      .... 
It  is  seen  that  the  values  of  a  and,  therefore,  of 


or   the 


concentration  of  the  ions  for  potassium  sulphate,  differ  widely 
from  those  for  either  aluminium  or  chromium  sulphate:  while, 
for  the  latter  sulphates,  the  values  of  n  show  an  almost  com- 
plete agreement  throughout  the  range  of  dilution  given.  The 
change  of  dissociation  or  ionization  produced  by  mixing  with 
potassium  sulphate  should,  therefore,  be  very  nearly  the  same 
in  both  cases,  if  we  neglect  the  effect  of  changes  in  volume 
which  in  this  case  are  extremely  small.  Reference  to  the  pre- 
ceding tables  I.  and  III.,  however,  shows  that  this  is  by  no 
means  the  case.  The  divergence  from  the  mean  is  four  or 
five  times  greater  in  the  case  of  the  chrome  alum  than  for  the 
aluminium  alum  at  the  same  dilution ,  or,  is  also  much  greater  if 
we  compare  them  at  equal  distances  from  the  point  of  satura- 

1  Ztschr.  phys  Chem.,  a,  491,  (1887). 


26 

tion.  Even  if  we  conclude,  therefore,  that  the  potassium 
aluminium  alum  is  entirely  dissociated  we  must  infer  that  the 
molecules  of  the  double  salt  in  a  concentrated  solution  of 
chrome  alum  are  only  partially  broken  down.  This  con?lu- 
sion  with  respect  to  chrome  alum  agrees  with  that  reached  on 
other  grounds  by  Carey  Lea,'  who  finds  by  the  use  of  a 
reagent  for  the  detection  of  free  sulphuric  acid  in  the  presence 
of  sulphates  that  chrome  alum  is  the  only  one  present  as  such 
in  .solution. 

In  order  to  find  whether  the  solution  of  an  alum  is  simply 
equivalent  to  a  mixture  of  solutions  of  its  equivalents,  a  num- 
of  mixtures  were  prepared  of  equal  volumes  of  solutions  of 
potassium  sulphate  and  aluminium  sulphate  of  the  same 
molecular  concentration  and  also  of  potassium  sulphate  and 
chromium  sulphate.  The  conductivities  of  the  constituents 
salts  were  observed,  then  that  of  the  mixtures.  The  results 
appear  in  the  following  tables  : 

Potassium  Sulphate  and  Aluminium  Sulphate. 


Gram- 
molecules 
per  litre. 

KjSO,. 

Alj(SO,),. 
/'t-25°. 

Mean. 

Differ- 
Mixture  observed,  eiice. 
0               Per 
/'„25   .            cent. 

0.2175 

170.2 

105.7 

137-9 

129. 1 

-6.4 

0.10855 

186.9 

130.3 

158.6 

I5I-8 

—4-3 

0.05427 

202.8 

153.6 

17S.2 

174.2 

— 2  .,2 

0.03333 

213.9 

172.5 

193-1 

190. 1 

—1.6 

0.01666 

229.1 

202.2 

215.6 

214.3 

—0.6 

Potassium  Sulphate  and  Chromium  Sulphate. 


Gram- 
olecules 
;)er  litre. 

KjSO,. 

Cr.j(SO,),. 
f^v25°. 

Mixture  observed. 
0 
Mean.            /'r25    . 

Difference 
Per  cent. 

0.333 

157-4 

94-2 

125.8 

II3-0 

lO.I 

0.25 

167.9 

107-3 

137-6 

125. 1 

—9.0 

O.I 

187.0 

139.0 

163.0 

155-1 

—4.9 

0.05 

205.1 

162.7 

183-9 

177-9 

—3-3 

0,025 

220.3 

190.7 

205.5 

202.8 

—  1.3 

1  Ztschr.  anorg.  Chem.,  4,  445,  (i893)- 


lie   potassium 


infer  that  the 
;(1   solution  of 

This  coii?lu- 
lat  reached  on 

the  use  of  a 
II  the  presence 
resent  as  such 

ilum  is  simply 
alents,  a  num- 
)f  solutions  of 
of  the  same 
sulphate  and 
e  constituents 
.     The  results 


Iphatc. 


Differ- 

jre  observed,  eiice. 
0               Per 
/'„25   .           cent. 

129. 1 

-6.4 

151-8 

—4-3 

174.2 

— 2.2 

1 90. 1 

—1.6 

214-3 

—0.6 

'phate. 

rved. 

Difference. 
Per  cent. 

0         - 

-lO.I 

I 

—9.0 

I 

—4.9 

9 

—3-3 

8 

—1-3 

27 

The  results  for  mixtures  of  potassium  and  aluminum  sul- 
phates show  a  close  agreement  with  those  obtained  for  the 
alum  ;  those  for  potassium  and  chromium  sulphates  show  a 
somewhat  remarkable  difference — the  alum  having  a  consid- 
erably lower  conductivity  at  corresponding  dilutions.  It  may 
be  remarked  that  volume-changes  play  an  unimportant  part 
in  this  instance  since,  according  to  Gerlach's  ob-servations,' 
the  contraction  at  15°  for  a  mixture  of  potassium  and  alumin- 
ium .sulphates  containing  0.21  gram-molecules  per  litre  is 
0.06  per  cent.,  and  for  a  mixture  of  potassium  and  chromium 
sulphates  containing  0.27  gram-molecules  per  litre  is  at  the 
same  temperature  0.12  per  cent.  If  the  difference  noticed  is 
well  founded,  it  might  be  accounted  for  by  supposing  that  the 
molecules  of  the  double  salt  remain  in  part  undissolved  when 
its  crystals  are  dissolved,  but  that  the  molecules  of  the  con- 
stituent salts  do  not  necessarily  unite  when  their  solutions 
are  mixed.  This  is  the  explanation  given  by  Graham'  of  the 
fact  observed  by  him  that  the  diffusion  of  the  double  sulphate 
of  potassium  and  magnesium  differed  from  that  of  a  mixture 
of  its  constituent  salts. 

Summary  of  Conductivity  Results. 
The  preceding  results  in  so  far  as  they  bear  upon  the  ex- 
istence of  alums  as  such  in  solution  may  be  summarized  as 
follows  : 

1.  The  alums  in  dilute  solution  are  entirely  dissociated  into 
their  constituent  salts. 

2.  In  concentrated  solution  they  have  a  lower  conductivity 
than  the  mean  conductivity  of  their  constituents.  The  differ- 
ence is  more  marked  as  the  concentration  increases  ;  and  is 
of  the  same  order  as  that  observed  for  other  double  sulphates, 
and  greater  than  that  observed  in  the  case  of  mixtures  of  sul- 
phates incapable  of  yielding  a  double  salt.  There  is,  there- 
fore, some  evidence  that  the  alums  are  partially  undissociated 
in  concentrated  solution. 

3.  The  amount  of  the  divergence  from  the  mean  conduc- 
tivity of  its  constituents  for  chrome  alum  as  compared  with 
the  aUtminium  alums  affords  strong  evidence  that  this  alum, 
at  least,  exists  as  such  in  solution. 


1  Ztschr.  anal.  Cbem.,  a8,  505,  (1889). 


••J  Phtl.  Trans.,  1850,  i. 


JF 


28 


Freezing- Point  Measurements. 

The  apparatus  used  in  tlie  freezing-point  observations  was 
of  the  ordinary  Beckmann  form,  except  that  the  inner  tube 
containing  the  sohitions  was  slightly  larger  in  diameter  to 
prevent  the  danger  of  the  stirrer  coming  into  contact  with  the 
thermometer,  and  had  no  side  branch.  The  ice-bath  was  in- 
cased with  felt.  The  solutions  used  were  made  up  from  the 
same  solutions  as  those  employed  in  conductivity  work.  In, 
every  freezing-point  determination  the  same  water  was  em- 
ployed as  that  used  in  making  up  the  solution  in  question. 

The  following  tables  show  the  freezing-point  lowenngs  ob- 
tained for  the  alums  and  their  constituent  salts.  The  follow- 
ing svmbols  are  used : 

G  denotes  the  number  of  grams  of  salt  dissolved  in  a  litre 

of  solution. 

N  denotes  the  number  of  gram-molecules  per  litre  of  solu- 

trion. 

L  denotes  the  corrected  lowering. 

A  denotes  the  gram-molecular  lowering. 

In  the  case  of  the  alums  the  double  formulas  are  used  for 
convenience  in  comparison  with  their  constituents,  the  sum 
of  the  lowerings  for  the  constituents  being  then  directly  com- 
parable with  the  lowering  of  the  alum. 

I.     K,SO,  [I74-34]- 

G.  N. 


No       G. 

I    37-857 


N.  I.. 

0.217       0.890°  4.10 

][8.9285  0.1086  0.466  4.29 

9.4643  0.0543  0.250  4-6i 

5.8110  0.0333  0.161  4.83 

2.9055  0.0167  0.084  5.03 


No. 

1  58.1134  0.333 

2  43-5850  0.250 

3  17-434  o.ioo 

4  8.717  0.050 

5  4-3585  0.025 


II.  A1,(S0,),  [342-34]- 


No.   G. 
I  44-740 

33-555 
22.370 

15-659 
8.948 

6. 711 

4-474 


2 
3 
4 

5 
6 

7 


N.      r.-  No. 

0.I3I  0.516°  3.94  I 

0.098   0.410  4.18  2 

0.0653  0.288  4.41  3 

0.0457  0.212  4.64  4 

0.0261  0.127  4.87  5 

0.0196  o.ioi  5-15 

0.0131  0.073  5-57 


N. 
0.217 


L. 

1.311° 
1.004 
0.432 
0.230 
0.122 


0.832° 


A. 


74-338 
37.169  0.1086  0.43b 
18.5845  0.0543  0.245 
II. 411  0.0333  0.189 
5-7055  0.0166  0.088 


3-93 
4.02 

4-32 
4.60 
4.88 

A. 

3-83 
4-03 
4-51 
4-77 
5-30 


29 


srvations  was 
he  inner  tube 
1  diameter  to 
ntact  with  the 
e-bath  was  in- 
;  up  from  the 
'ity  work.  In, 
vater  was  em- 
iti  in  question, 
lowerings  ob- 
.     The  follow- 

)lved  in  a  litre 

;r  litre  of  solu- 


is  are  used  for 
Luents,  the  sum 
n  directly  com- 


f. 

L. 

133 

1.3"" 

3-93 

!50 

1.004 

4.02 

GO 

0.432 

4-32 

),SO 

0.230 

4.60 

>25 

0.122 

4.88 

L. 

J. 

17 

0.832° 

3.83 

o86 

0.438 

4-03 

543 

0.245 

4-51 

333 

0.189 

4.77 

1 66 

0.088 

5-30 

III.     Cr,(SO.),  [392.58]. 


No. 

G. 

N. 

I,. 

^■J. 

I 

130.860 

0.333 

•     •    •    • 

.... 

2 

98.145 

0.250 

1.029" 

4.12 

3 

39.258 

O.IOO 

0.417 

4.17 

4 

19.629 

0.05 

0.230 

4.60 

5 

9.8145 

0.025 

O.I2I 

4-84 

IV. 

(NH,),SO, 

[132.16]. 

No. 

(.. 

N, 

I- 

J. 

I 

26.432 

0.2 

0.829° 

4-145 

2 

13.216 

O.I 

0.437 

4370 

3 

9.2512 

0.07 

0.316 

4-514 

4 

6.608 

0.05 

0.237 

4-740 

5 

3.9648 

0.03 

0.148 

4-933 

6 

1.9824 

0.015 

0.075 

5.00 

V.     K,A1,(S0J,-|-24H,0  [948.8 

2]- 

No. 

G. 

N. 

I-. 

J. 

I 

47-441 

0.05 

0.409° 

8.18 

2 

35.5807 

0.0375 

0.320 

8-53 

3 

23.720 

0.025 

0.222 

8.88 

4 

"•8575 

0.0125 

0.120 

9.60 

5 

4- 7430 

0.005 

0.057 

11.40 

VI.     Na,Al,(SO,).  +  24H,0  [916 

66] 

No. 

G. 

N. 

h. 

J. 

I 

22.9165 

0.025 

0.229° 

9.16 

2 

11.4582 

0.0125 

0.125 

10.00 

3 

5.7291 

0.00625 

0.009 

11.04 

VII.     (NH,), 

Al,(SO.),  +  24H,0  [906.6]. 

No. 

G. 

N. 

I-. 

J. 

I 

45-330 

0.05 

0.408° 

8.16 

2 

33-997 

0.0375 

0.318 

8.48 

3 

22.665 

0.025 

0.224 

8.96 

4 

"•332 

0.0125 

O.I2I 

9.68 

5 

5.666 

0.00625 

0.066 

10.56 

VIII.     K,Cr,(SOJ,  +  24H,0  [999]- 

No. 

G. 

N. 

h. 

^. 

I 

117.44 

O.II7 

0.888° 

7-59 

2 

88.08 

0.088 

0.686 

7.80 

3 

58.72 

0.059 

0.480 

8.14 

4 

29.36 

0.0294 

0.267 

9.08 

5 

17.618 

0.0176 

0.170 

9.66 

6 

11.744 

O.OII7 

O.II9 

10.17 

7 

5872 

0.0059 

0.065 

11.02 

30 


IX.  (NH,),Cr,(SOJ,  +  24H,0  [956.8I. 


No. 
I 

2 

3 
4 

5 

6 


No. 
I 

2 

3 

4 

5 
6 

7 
8 


G. 

92.740 

46., -,70 
27.822 
16.6932 
I  1. 1  288 
5-5644 


X. 


N. 
0.097 
0.0484 
0.0291 
0.0174 

o.oi 16 
0.0058 


0.768° 

0.400 
0.266 

0.168 
0.II7 
0,064 


J. 
7.92 
8.26 
9.14 
9-65 

10.09 
11.04 


(NH,),Fe,(SO,).  +  24H,0  r964.42]-^ 

7.08 


G. 
247.72 

185-79 
123-86 
92.895 
61.930 
37-158 
24.772 
12.386 

6.193 


N. 

0.257 

0.192 

0.128 

0.096 

0.064 

0.0385 

0.0257 

0.0128 

0.0014 


U. 
1.820° 
1.400 
0.927 
0.713 
0.505 
0.322 
0.227 
O.I2I 
0.066 


7.29 
7-24 

7-43 
7-89 
8.36 
8.83 

9-45 
10.31 


Comparison  of  freeziyig- Point  Resxdts. 

Comparing  the  results  for  the  different  alums  as  shown  in 
the  foregoing  tables,  it  will  be  seen  that,  as  regards  theahunm- 
um  alums  the  soda  alum  (Table  VI)  gives  a  greater  de- 
;rssrd:  fo;  corresponding  dilutions  tljan  either  potass.urn 
(Table  V)  or  ammonium  alum  (Table  VII),  whi  e  the 
depressions  given  by  potassium  alum  correspond  closel>^ 
XI  are  slightly  larger  in  concentrated  solution  than 
ule    for    tl^    Limonium    alum.       For    dilute     solutions 

"reverse  is  the  case;  but  the  experimenta  error  is 
here  greater  and  less  value  is  to  be  attached  to  the  resul^^ 
The  ammoniun  chrome  and  potassium   chron.e  alums  alo 

show  closely  corresponding  values  for  corresponding  dilutions 

(Tablec  VIII.  IX),  while  these  values  are  somewhat  g  eater 

or  corresponding  dilutions  than  thoseof  the  aluminium  alums 
In  the  following  tables  is  shown  a  comparison  of  the  lower- 

ings  given  by  the  alums  with  the  sum  of  the  lowenngs  for 
1^?  r'c onstituents  at  the  same  dilution.     The  values  for  the 

constituent  salts  are  interpolated  from  the  preceding  tables  I 

to  IV. 


31 


6.8]. 


Potassium  Aluminium  Alum. 


A. 

7.9a 
8.26 

9.14 

965 
10.09 
11.04 


4.42]. 


J. 
7.08 
7.29 
7.24 
7-43 
7-89 
8.36 
8.83 

9-45 
10.31 

mlts. 

US  as  shown  in 
;ardsthealumin- 
es  a  greater  de- 
iither  potassium 
^11),    while  the 
rrespond  closely, 
[    solution     than 
dilute     solutions 
imental    error    is 
d  to  the  results, 
rome  alums  also 
ponding  dilutions 
somewhat  greater 
iluminium  alums, 
rison  of  the  lower- 
the  lowerings  for 
bie  values  for  the 
)receding  tables  I 


No. 

I 
2 
3 
4 


No. 
I 

2 

3 
4 


No. 


No. 
I 
2 

3 
4 


N. 
0.05 
0.0375 
0.025 
0.0125 


4.61 
4.76 
4.89 
5.02 


,(SO,),. 

J. 

Sum. 

PotHSsium 
alum. 

Z/  obaerveU 

Differ 
eiice. 

4.60 

9.21 

8.18 

1.03 

4.72 

9.48 

8.53 

0.95 

4.91 

9.80 

8.88 

0.92 

5-61 

10,63 

9.60 

1.03 

Ammonium  Aluminium  Alum. 


N. 
0.05 
0.0375 
0.025 
0.0125 


(N11,),S04. 
J. 

4-74 
4.86 

4-95 
5.02 


Al,(SO,), 
J. 

4-55 
4.72 
4. ox 

561 


Sum. 
9.29 

9-58 

9.86 

10.63 


Potassium  Chrome  Alum. 


N. 
O.II7 
0.088 
0.059 
0.0294 


K,SO,. 
J. 


CrjCSO,),. 
J. 


4.28  4.16 

4.38  4.27 

4-54  4-51 

4.83  4.80 


Sura. 
8.44 
8.65 
905 
9-63 


Amm.-A'.. 

alum. 

A  observed. 

8.16 

8.48 

8.96 

9.68 


K-Cr  alum. 
A  observed. 

7-59 
7.80 
8.14 
9.07 


Ammonium  Chrome  Alum. 


(NH4),SO,. 
J. 


Cr,(SO,),. 
J. 


Sum. 


Amm.-Cr  alum. 
A  observed. 


7.92 
8.26 


Differ- 
ence. 

1.I3 

1. 10 

0.90 

0.95 


Differ- 
ence. 

0.85 
0.85 
0.91 
0.55 


Differ- 
ence. 


0.65 
I. II 
0.00 


1  0.097  4-38  4-19  8.57 

2  0.0484  4.76  4.61  9.37 

3  0.0291  4.93  4-8i  9-74  9H 

These  tables  show  that  for  the  most  concentrated  solutions  the 
lowerings  given  by  the  alums,  with  the  exception  of  ammo- 
nium chrome  alum,  is  uniformly  10  or  11  per  cent,  less  than 
he  sum  of  the  lowerings  for  its  components 


The  abnormal 


■"f-yj*-);^.-- 


32 

value  for  ammonium  chrome  alum— giving  7.3  per  cent.— may 
be  attributed  to  experimental  error,  since  the  other  values  ob- 
tained for  it  are  in  agreement  with  those  of  the  other  alums. 
Raoult'  found  for  potassium  aluminium  alum  a  lowering  of  1.2 
per  cent,  less  than  the  sum  of  those  obtained  for  itscomponents, 
and  he  inferred  that  its  dissociatfon  was  con.plete.  He  does 
not,  however,  state  the  concentration  observed  ;  and  the  ex- 
tent to  which  the  difference  obtained  depends  upon  concen- 
tration is  apparent  from  the  above  table.  These  results  must 
be  regarded  as  comfirming  the  indications  given  by  conduc- 
tivity of  the  existence  of  alum  molecules  in  concentrated 
solution. 

II. 
Double  Chloride  of  Zinc  and  Potassium. 
Riidorff'  distinguished,  as  has  already  been  mentioned,  two 
classes  of  double  chlorides.  ( 1 )  those  which  suffer  decompo- 
sition in  water  solution,  and  (2)  those  which  remain  undecom- 
posed.  The  first  class  are  to  be  regarded  as  double  salts  of 
the  same  type  as  the  alums.  The  second  class  he  regards  as 
true  binary  compounds.  The  following  examples  of  the  first 
class  are  given  : 

2KCI+CUCI, -f  2H,0 
2NH,Cl  +  CuCl,+  2H,0 
2KCH-ZnCl,-+-H,0 
KCH- MgCl,  4- 6H,0 
2NaCl+CdCl,+  3H,0 
BaCl,  +  CdCl,  +  4H,0. 

It  seemed  of  interest  in  connection  with  the  foregoing  in- 
vestigation to  study  an  example  of  this  class  by  the  con- 
ductivity method.  For  this  purpose,  the  double  chloride  of 
potassium  and  zinc,  2KCl.ZnCl,+  H,0  was  selected. 

Preparation, 

In  preparing  the  double  chloride  of  potassium  and  zinc, 
potassium  chloride  was  used  which  had  been  twice  crystal- 
lized, and  was  shown  by  the  flame  test  to  be  free  from 
sodium.     The  zinc  chloride  used  was  tested  and  found  free 

I  Compt.  reud.,  vy,  9>4.  (>884).  »  Ber.  d.  chem.  Ges.,  ai.  3048.  (1888). 


er  cent. — may 
her  values  ob- 
other  alums, 
oweringof  1.2 
iscomponents, 
te.  He  does 
;  and  the  ex- 
upon  concen- 
e  results  must 
:n  by  conduc- 
i  concentrated 


nentiLdied,  two 
uffer  decompo- 
nain  undecom- 
iouble  salts  of 
he  regards  as 
pies  of  the  first 


;  foregoing  in- 
ss  by  the  con- 
ble  chloride  of 
elected. 


isium  and  zinc, 
I  twice  crystal- 
3  be  free  from 
and  found  free 

11,3048,  (1888). 


33 

from  impurities.  The  two  chlorides  were  brought  together  in 
solution  in  the  proportion  necessary  to  form  the  double  salt, 
and  the  solution  evaporated  to  crystallization.  The  salt  was 
separated  as  rapidly  as  possible  from  its  mother-liquor  on  the 
filter-pump,  and  dried  under  a  press.  A  specimen,  previ- 
ously dried  at  130",  was  immediately  weighed  off,  and  an- 
alyzed for  zinc. 
The  analysis  gave  : 

Percentage  of  zinc  found 22.91 

"  calculated  for  2KCl.ZnCl,  .  22.94 

The  solution  was  standardized  by  precipitating  zinc  by  so- 
dium carbonate  and  weighing  as  zinc  oxide. 
The  conductivity  results  are  tabulated  below : 
2KCl.ZnCl,  [285.58]. 


Gram- 
molecules 
per  litre. 

Litres 
per  Kram- 
molecule. 

0.2 

0.5 

O.I 

I.O 

0.5 

3.0 

0.25 

4.0 

0.05 

20.0 

0.025 

40.0 

0.005 

200.0 

0.0025 

400.0 

0.0005 

2000.0 

0.00025 

4000.0 

0.00005 

20000.0 

I. 

11. 

«:.25°. 

f^v2f. 

Mean. 

117. 2 

•    •    •    • 

117. 2 

176.0 

•    •    •    • 

176.0 

244.2 



244.2 

303.7 

.... 

303-7 

397-4 

397-2 

397-3 

426.2 

423.8 

425-3 

468.4 

469.0 

468.7 

483.2 

484.2 

483-7 

504.0 

504.6 

504-3 

510.8 

512.3 

5"-5 

516.8 

509.0 

512.9 

518.8 

516.0 

517-4 

0.000025  40000.0 

A  comparison  of  the  conductivity  of  the  double  salt  with 
the  conductivities  of  its  constituents  is  given  below.  The 
values  for  zinc  chloride  and  potassium  chloride  are  interpo- 
lated from  the  tables  of  Kohlrausch'  and  reduced  to  25°.  The 
molecular  conductivity  of  the  zinc  chloride  is  taken  at  the 
same  volume  as  the  double  salt.  That  of  potassium  chloride 
is  taken  as  twice  the  molecular  conductivity  of  potassium 
chloride  at  one-half  the  volume  of  the  double  salt. 

1  Wied.  Ann.  J6,  i6i,  (1885). 


■ffrii iLiiff  iieii i,uwiiir  1.*^ -' -^.- 


rj#j" 


Double  Ch'iride  of  Zinc  and  Potassium. 


Utresper  Uii-sper 

gram-mol*-         K  :i         KH<f»-">o'« 

cult  v>  ^         cvile 

orKCl.     2X/-25  .o(ZuCl,. 


0.5 

I.O 

2.0 

lO.O 

20.0 

1CX3.0 

200.0 

lOOO.O 

2000.0 

lOOOO.O 


196. '• 

211. a 

?2t  ,6 

241.4 

3;  J.C 
2''H.8 
269  o 

2754 

277  6 

27  JO 


O,  I 

2.0 

4.0 

20.0 
40.0 

20O.C' 

4UO.O 
iooo.o 
4000  o 

2C00C).0 


/.nCl,. 
)"t-25°. 

78.4 

120.0 

140.3 
179.2 
186.7 
213.6 

220.1 

232.0 

234.8 

240.2 
240.7 

The  foregoing  comparison  leaves  no  room  for  doubt  as  to 
the  existence  of  thi-i  double  salt  as  such  in  concentrated  solu- 
tion, while  at  a  dilution  of  between  1000  and  2000  liters  it  is 
entirely  dibsociated  into  its  constituents. 

Conclusion. 
Regarding  the  doable  chloride  of  zinc  a^id  potassium  as  a 
type  of  the  class  of  dissociated  double  haloids,  we  may  draw 
the  conclusion  that  the.se  salts  are  present  as  such  in  their 
concentrated  solutions  As  compared  with  the  alums,  they 
show  a  greater  degree  of  stability  towards  water  in  concen- 
trated solutions,  bet,  i.'.  dilute  solutions,  resemble  them  in 
becoming  wholly  dissociated  into  their  component  salts. 


2C1K0OO.O      280.0     40000.0 


Sum. 
274.4 

33«-8 
361.9 
420.6 

436.7 
478.4 
489.1 

507-4 
512.4 
519.2 
520.7 


iKCI.ZnCI, 
observed, 

176.0 

244.2 
303.7 

397-3 
425.3 
468.7 

483.7 
504.3 
5" -5 
512.9 
517-4 


Dtfler- 
enc"?. 

98.4 
87.6 

58.2 

23-3 
II.4 

9-7 
5.4 

3.1 
0.9 

6.3 
3-3 


I.ZnCI, 
•rved, 

25°. 
^6.0 

33-7 
37-3 
25-3 

68.7 

83.7 
04.3 
"•5 
12.9 

17.4 

r  doubt  as  to 
intrated  solu- 
00  liters  it  is 


tassium  as  a 
we  may  draw 
such  in  their 
;  alums,  they 
er  in  concen- 
nble  them  in 
nt  salts. 


Difller- 

98.4 
87.6 
58.2 

23-3 
11.4 

9-7 
54 
31 
0.9 

6.3 
3-3 


I 


BIOGRAPHICAL. 

The  author  is  a  native  of  Plainfield,  Nova  Scotia,  where 
he  was  born  January  24,  1864.  He  graduated  as  Bachelor  of 
Arts  from  Dalhousie  College,  Halifax,  N.  S.,  in  1886,  and 
thereafter  occupied  a  position  as  ateachor  in  the  High  School, 
New  Glasgow,  N.  S.,  until  1892.  In  October,  1892,  he  en- 
tered the  Johns  Hopkins  University,  where  he  has  since  been 
pursuing  a  post-graduate  course  in  Chemistry,  Physics,  and 
Mathematics.  He  was  awarded  a  University  scholarship  in 
Chemistry  in  January,  1895,  and  was  appointed  a  Fellow  in 
June  of  the  same  year. 


A  CONTRIBUTION 


ro  TJKB  HtiroY  Of 


DOUBLE  8ftl,T8  IN 


DISSERTATION 


■'  v^'  v.-  „  ;, '.  ■■  V-  y.- 1  ■;  -  ■      ■■■.-■■  >     -.■  .    ■ 


^—»X- 


E:BEN,-K2:ER'  MJ>kGlKjkX 


11196 


4 


■'■.     !■•  ■  ■  ■  ■    .1    '  ■ 


tit-.'S'.y  ft  '■-' si"'.' '»" 


